The cylinder head joint is a critical sealing joint in an internal combustion engine, particularly in high compression diesel engines. In addition to the typical sealing problems encountered at the cylinder head joint, such as preventing blowout of the combustion gas seal or wire ring while maintaining a coolant and/or oil tight head seal, diesel engines that employ flanged cylinder liners further complicate sealing of the cylinder head joint. For example, to avoid high unit loadings and associated crack initiation where the flange of the cylinder liner engages the engine block, a spacer plate or plates are provided in the cylinder head joint between the cylinder head and block. The spacer plates provide clearance for the flange of the cylinder liner to be mounted on the cylinder block in the cylinder head joint, rather than in a counter bore of the cylinder block, to reduce crack initiation in the cylinder block. Additionally, the spacer plates distribute mechanically induced cylinder head loads into the cylinder block without concentrating the loads on any one part of the cylinder block; i.e., the liner flange to cylinder block interface. Typically, the spacer plates are constructed of a thermally conductive material such as aluminum to distribute thermally induced cylinder head loads and reduce high thermal unit loading of the cylinder block.
Presently, diesel engines employing flanged cylinder liners and spacer plates at the cylinder head joint have required gaskets clamped both between the cylinder block and spacer plate and between the spacer plate and cylinder head. These gaskets are shaped similar to the spacer plate and, for combination head gaskets with integral combustion gas seals, seal combustion gasses within the cylinder liner and both coolant and/or oil between the cylinder block and head. Although these gaskets adequately seal across the cylinder head joint, they nevertheless can be subject to leakage due to thermal loading during engine transients. Further, due to varying tolerances of the gaskets, the loading across the cylinder head joint can vary.
As a result of these and other sealing difficulties, various gaskets have been developed in an attempt to improve sealing of the cylinder head joint. For example, U.S. Pat. No. 5,125,551 to Slee discloses a combination cylinder head gasket and combustion gas seal which includes heat conductive elements between integral metal fire rings in an attempt to reduce thermal loading of the gasket. However, the cylinder head gasket disclosed in U.S. Pat. No. 5,125,551 adds complexity and cost while still being susceptible to failure due to non-uniform heating during engine operation.
As another example, the combination cylinder head gasket and combustion gas seal shown in U.S. Pat. No. 5,125,375 to Vuk is adapted for use with a specially machined cylinder liner in an attempt to resist blowout of the integral combustion gas seal. The flange of the cylinder liner is machined frustoconical and cooperates with the cylinder head to produce a wedging action that resists radial expansion of the combustion gas seal when clamped between the cylinder head and liner. Aside from the machining difficulty involved in creating the frustoconical contour, the gasket disclosed in U.S. Pat. No. 5,125,375 relies on a preset clearance between the cylinder flange and cylinder head to provide the necessary wedging action with the frustoconical contour. Should the cylinder head be improperly assembled or should the preset clearance become insufficient due to creep of the combustion gas seal, the gasket can be subject to blowout.
A cylinder head gasket that combines a flexible sealing element with a metal gasket body to prevent detachment of the sealing element from the gasket body is shown in U.S. Pat. No. 5,033,189 to Desverchere et al. Flexible sealing elements on either side of the metal gasket body are joined together through slots in the metal gasket body to reduce the risk of the sealing elements becoming detached therefrom. One disadvantage of this construction is that the flexible sealing element is formed integral with the metal gasket body, thus requiring the entire gasket body to be discarded should a portion of the flexible sealing element fail.
What is needed is an improved gasket and gasket sealing system for use in the cylinder head joint of an internal combustion engine that overcomes the aforementioned deficiencies of the gaskets disclosed in U.S. Pat. Nos. 5,125,375, 5,033,189 and 5,125,551. Such a gasket sealing system should be compatible with diesel engines employing flanged cylinder liners and spacer plates at the cylinder head joint. Ideally, such a gasket sealing system should be inexpensive to manufacture and easily installed and, together with the spacer plate, should reduce thermal loading from the cylinder head to the combustion gas seal and cylinder block or liner.